Storage device communicating with host according to multicast communication protocol and communication method of host

ABSTRACT

A storage device includes a memory device; and a controller configured to fetch a command from a host, the command indicating a logical address, process the command based on the logical address, and receive, from a first replica storage device, an acknowledgment signal indicating that the command has been processed by the first replica storage device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. non-provisional application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2017-0121411, filed on Sep. 20,2017, in the Korean Intellectual Property Office, the entire contents ofwhich are incorporated herein by reference.

BACKGROUND 1. Field

At least some example embodiments of the inventive concepts disclosedherein relate to a storage device and a communication method of a host,and more particularly, relate to a storage device communicating with thehost according to a multicast communication protocol and a communicationmethod of the host.

2. Related Art

A flash memory device is being used as voice and image data storagemedia of information devices such as a computer, a smartphone, apersonal digital assistant (PDA), a digital camera, a voice recorder, anMP3 player, and a handheld PC. An example of a flash memory based massstorage device is a solid state drive (hereinafter referred to as“SSD”). An interface of the SSD should provide an optimal speed andreliability depending on various purposes of the SSD. To satisfy suchrequirements, interfaces such as a serial AT attachment (SATA)interface, a PCI Express (PCIe) interface, and a serial attached SCSI(SAS) may be used as the optimal SSD interface. In particular, aPCIe-based NVM express (NVMe) is studied and applied.

A host may communicate with a plurality of SSDs for distributing andmanaging data. The host may communicate with SSDs according to a peer topeer (P2P) communication method. However, if the host provides a commandto any one of the SSDs according to the P2P communication method, an SSDthat receives the command has to provide the received command to anotherSSD, thereby causing an increase in a time (i.e., a latency) taken toprocess the command. Also, a memory space is necessary for each SSD toprovide a command to any other SSD and receive completion information ofthe command.

SUMMARY

At least some example embodiments of the inventive concepts provide astorage device communicating with a host according to a multicastcommunication protocol and a communication method of the host.

According to at least some example embodiments of the inventiveconcepts, a storage device includes a memory device; and a controller,the controller being configured to fetch a command from a host, thecommand indicating a logical address, process the command based on thelogical address, and receive, from a first replica storage device, anacknowledgment signal indicating that the command has been processed bythe first replica storage device.

According to at least some example embodiments of the inventiveconcepts, a storage device includes a memory device; and a controller,the controller being configured to, fetch a command from a host, thecommand indicating logical address; process the command based on thelogical address; and transmit, to a master storage device, anacknowledgment signal indicating that the command has been processed.

According to at least some example embodiments of the inventiveconcepts, a communication method of a host connected with first andsecond storage devices includes generating a command for controlling thefirst and second storage devices; causing the first and second storagedevices to fetch the command by updating at least a register of thefirst storage device; and receiving completion information of thecommand from the first storage device when the command is processed inthe second storage device and the second storage device transmits anacknowledgment signal indicating that the command is processed to thefirst storage device.

BRIEF DESCRIPTION OF THE FIGURES

The above and other features and advantages of example embodiments ofthe inventive concepts will become more apparent by describing in detailexample embodiments of the inventive concepts with reference to theattached drawings. The accompanying drawings are intended to depictexample embodiments of the inventive concepts and should not beinterpreted to limit the intended scope of the claims. The accompanyingdrawings are not to be considered as drawn to scale unless explicitlynoted.

FIG. 1 is a block diagram illustrating a storage system according to atleast some example embodiments of the inventive concepts.

FIG. 2 is a block diagram illustrating a host illustrated in FIG. 1.

FIG. 3 is block diagram illustrating a storage device illustrated inFIG. 1.

FIG. 4 is a flowchart illustrating a multicast communication methodbetween the host and storage devices, according to at least some exampleembodiments of the inventive concepts.

FIG. 5 is a flowchart illustrating a multicast communication methodbetween the host and the storage devices, according to at least someexample embodiments of the inventive concepts.

FIG. 6 is a flowchart illustrating a multicast communication methodbetween the host and the storage devices, according to at least someexample embodiments of the inventive concepts.

FIG. 7 is a view illustrating a change of master devices with respect todata according to a change in setting values of a controller accordingto at least some example embodiments of the inventive concepts.

FIG. 8 is a flowchart illustrating a process of determining a newreplica storage device when an operation of a second storage deviceoperating as a replica storage device of first to third storage devicesgoes down.

FIG. 9 is a flowchart illustrating a multicast communication methodbetween the host and the storage devices after a first controllerdetermines the third storage device as a new replica storage device.

FIG. 10 is a flowchart illustrating a process of determining a newmaster storage device when an operation of the first storage deviceoperating as a master storage device of the first to third storagedevices goes down.

FIG. 11 is a flowchart illustrating a multicast communication methodbetween a host and storage devices after second and third controllersdetermine a second storage device as a new master storage device.

FIG. 12 is a view illustrating that a vector command is transmitted fromthe host to the storage devices depending on a multicast communicationprotocol according to at least some example embodiments of the inventiveconcepts.

FIG. 13 is a block diagram illustrating the storage system according toat least another example embodiment of the inventive concepts.

FIG. 14 is a view illustrating the computing system according to atleast some example embodiments of the inventive concepts.

FIG. 15 is a block diagram illustrating a user system to which amulticast communication method according to at least some exampleembodiments of the inventive concepts is applied.

DETAILED DESCRIPTION

As is traditional in the field of the inventive concepts, embodimentsare described, and illustrated in the drawings, in terms of functionalblocks, units and/or modules. Those skilled in the art will appreciatethat these blocks, units and/or modules are physically implemented byelectronic (or optical) circuits such as logic circuits, discretecomponents, microprocessors, hard-wired circuits, memory elements,wiring connections, and the like, which may be formed usingsemiconductor-based fabrication techniques or other manufacturingtechnologies. In the case of the blocks, units and/or modules beingimplemented by microprocessors or similar, they may be programmed usingsoftware (e.g., microcode) to perform various functions discussed hereinand may optionally be driven by firmware and/or software. Alternatively,each block, unit and/or module may be implemented by dedicated hardware,or as a combination of dedicated hardware to perform some functions anda processor (e.g., one or more programmed microprocessors and associatedcircuitry) to perform other functions. Also, each block, unit and/ormodule of the embodiments may be physically separated into two or moreinteracting and discrete blocks, units and/or modules without departingfrom the scope of the inventive concepts. Further, the blocks, unitsand/or modules of the embodiments may be physically combined into morecomplex blocks, units and/or modules without departing from the scope ofthe inventive concepts.

At least some example embodiments of the inventive concepts provide acomputing system for providing high security and reliability of firmwareby using a hardware security module and a firmware managing methodthereof.

FIG. 1 is a block diagram illustrating a storage system according to atleast some example embodiments of the inventive concepts. Referring toFIG. 1, a storage system 10 may include a host 11, a first storagedevice 12, and a second storage device 15.

The host 11 may write data in the first storage device 12 or may readdata from the first storage device 12. To this end, the host 11 maygenerate various commands to control the first storage device 12. Ingeneral, a command processing process of the host 11 is as follows. Thehost 11 may transmit a command to the first storage device 12 and mayreceive completion information and an interrupt, which are associatedwith the transmitted command, from the first storage device 12. The host11 may perform interrupt processing for completing a thread or a taskassociated with the transmitted command, in response to the interrupt.

The first storage device 12 may fetch a command that the host 11generates. Depending on the command generated by the host 11, the firststorage device 12 may store data or may transmit data to the host 11.The second storage device 15 may back up data for coping with the eventthat an operation of the first storage device 12 goes down or that thefailure occurs in the first storage device 12. That is, the firststorage device 12 may be a master storage device, and the second storagedevice 15 may be a replica storage device. One of at least two storagedevices may be a master device, and the other thereof may be a replicastorage device. The master storage device may manage any other storagedevice except itself and may notify the host 11 that a command iscompleted. The replica storage device may back up or copy data that themaster storage device stores and may notify the master device of its owntask or processing state.

In the present disclosure, an operation of a storage device “going down”is synonymous with, and may also be referred to as, the storage devicemalfunctioning and/or the storage device having stopped operating.

The first storage device 12 may include a controller 13 and a memorydevice 14. The controller 13 may process a command that the host 11generates, by storing data in the memory device 14 or reading data fromthe memory device 14. The memory device 14 may store or output databased on control of the controller 13.

The second storage device 15 may include a controller 16 and a memorydevice 17. For example, the second storage device 15 may be implementedto be the same as the first storage device 12. The controller 16 and thememory device 17 may operate in a manner similar to the controller 13and the memory device 14 of the first storage device 12. As in the firststorage device 12, the second storage device 15 may fetch a command thatthe host 11 generates.

According to at least some example embodiments of the inventiveconcepts, the host 11 may transmit a command to at least two storagedevices such as the first and second storage devices 12 and 15. That is,the host 11 may multicast a command to the first and second storagedevices 12 and 15.

The first and second storage devices 12 and 15 may fetch a command thatthe host 11 generates, in parallel. In the example illustrated in FIG.1, the first storage device 12 is a master storage device and the secondstorage device 15 is a replica storage device. However, unlikeillustration, depending on a command that the host 11 generates, thefirst storage device 12 may be a replica storage device, and the secondstorage device 15 may be a master storage device. That is, roles of thefirst and second storage devices 12 and 15 may be changed according to acommand that the host 11 generates.

Even though the host 11 multicasts a command to the first and secondstorage devices 12 and 15, whether any device of the first and secondstorage devices 12 and 15 is a master storage device may not beimportant. Any one of the first and second storage devices 12 and 15 mayperform a role of a master storage device on data that the host 11requests, and the other thereof may perform a role of a replica storagedevice. To determine a master storage device and a replica storagedevice may be performed by the first and second storage devices 12 and15. That is, each of the first and second storage devices 12 and 15 maydetermine its own role based on a command that the host 11 generates. Aphysical configuration of the host 11 will be described below.

FIG. 2 is a block diagram illustrating a host illustrated in FIG. 1.FIG. 2 will be described with reference to FIG. 1. Referring to FIG. 2,a host 100 may include a processor 110, a host memory 120, and aninterface circuit 130.

The processor 110 may execute a variety of software (e.g., anapplication program, an operating system, and a device driver) loaded onthe host memory 120. The processor 110 may execute an operating system(OS) and an application program. The processor 110 may be a homogeneousmulti-core processor or a heterogeneous multi-core processor.

An application program or data to be processed by the processor 110 maybe loaded on the host memory 120. In more detail, a submission queue SQfor managing a queue for a command to be transmitted to the first andsecond storage devices 12 and 15 (refer to FIG. 1) and a completionqueue CQ for managing a queue for completion information of atransmitted command may be loaded on the host memory 120. A specificarea of the host memory 120 may be allocated in advance for thesubmission queue SQ and the completion queue CQ. The submission queue SQand the completion queue CQ may be referred to as a “circular buffer”.

The submission queue SQ that is a queue of submission entries written bythe host 100 may correspond to commands to be transmitted to the firstand second storage devices 12 and 15. The completion queue CQ that is aqueue of completion entries written by any one of the first and secondstorage devices 12 and 15 may indicate whether a command requested bythe host 100 is completed or completion information.

The submission queue SQ may be written or supplied by the host 100 andmay be fetched or consumed by the first and second storage devices 12and 15. A tail pointer TP of the submission queue SQ may be updated bythe host 100, and a location of a new tail pointer TP may be transmittedto the first and second storage devices 12 and 15 by the host 100. Anyone of the first and second storage devices 12 and 15 may transmitcompletion information, and thus, a head pointer HP of the submissionqueue SQ may be updated.

The completion queue CQ may be written or supplied by the first andsecond storage devices 12 and 15 and may be processed or consumed by thehost 100. A tail pointer TP of the completion queue CQ may be updated byany one of the first and second storage devices 12 and 15. The host 100may progress the head pointer HP of the completion queue CQ in responseto an interrupt transmitted from any one of the first and second storagedevices 12 and 15, and a location of a new head pointer HP may betransmitted to the first and second storage devices 12 and 15.

The interface circuit 130 may provide a physical connection between thehost 100 and the first and second storage devices 12 and 15. That is,the interface circuit 130 may convert a command, an address, data, etc.corresponding to various access requests issued from the host 100depending on a way to interface with the first and second storagedevices 12 and 15. A communication protocol of the interface circuit 130may include at least one of a universal serial bus (USB) protocol, asmall computer system interface (SCSI) protocol, a PCI express protocol,NVM express (NVMe) protocol, an ATA protocol, a parallel ATA (PATA)protocol, a serial ATA (SATA) protocol, and a serial attached SCSI (SAS)protocol. According to at least one example embodiment of the inventiveconcepts, an NVM express (NVMe) protocol for exchanging data in a PCIemanner may be applied to the interface circuit 130. A physicalconfiguration of the first and second storage devices 12 and 15 of FIG.1 will be described below.

FIG. 3 is block diagram illustrating a storage device illustrated inFIG. 1. FIG. 3 will be described with reference to FIG. 1. Aconfiguration of a storage device 200 illustrated in FIG. 3 may be aconfiguration of each of the first and second storage devices 12 and 15of FIG. 1. Referring to FIG. 3, the storage device 200 may includememory devices 211 to 213, a controller 220, and a buffer memory 240.

The memory devices 211 to 213 may perform a data input/output undercontrol of the controller 220. For example, each of the memory devices211 to 213 may include a volatile memory such as a dynamic random accessmemory (DRAM) or a static random access memory (SRAM) or a nonvolatilememory such as a NAND flash memory, a NOR flash memory, a resistiverandom access memory (ReRAM), a ferroelectric random access memory(FRAM), a phase change random access memory (PRAM), a thyristor randomaccess memory (TRAM), or a magnetic random access memory (MRAM). Thenumber of memory devices and the number of channels illustrated in FIG.3 are examples and at least some example embodiments of the inventivecomments are not limited thereto.

The controller 220 may provide an interface between the host 11 (referto FIG. 1) and the storage device 200. The controller 220 may include aprocessor 221, a host interface circuit 222, a storage device interfacecircuit 226, a buffer manager 229, and an internal memory interfacecircuit 230.

The processor 221 may control operations of internal components of thecontroller 220. The processor 221 may provide a variety of controlinformation, which is needed to perform a read operation or a writeoperation for the memory devices 211 to 213, to the host interfacecircuit 222, the storage device interface circuit 226, the buffermanager 229, and the internal memory interface circuit 230. Theprocessor 221 may operate depending on firmware provided for variouscontrol operations of the controller 220. For example, the processor 221may execute a flash translation layer (FTL) for performing a garbagecollection operation, an address managing operation, a wear levelingoperation, etc. for managing the memory devices 211 to 213.

The host interface circuit 222 may communicate with the host 100. Forexample, the host interface circuit 222 may include a first register 223for writing a submission queue tail doorbell SQTDBL of the host 100. Thehost interface circuit 222 may further include a second register 224 forwriting a completion queue head doorbell CQHDBL of the host 100. Thefirst register 223 may store information of a submission queue SQ of thehost 100, and the second register 224 may store information of acompletion queue CQ of the host 100. The submission queue tail doorbellSQTDBL may indicate a value of a tail pointer of a submission queue, andthe completion queue head doorbell CQHDBL may indicate a value of a headpointer of a completion queue. The host interface circuit 222 mayfurther include a third register 225 for storing an interrupt (IR) tableto manage interrupts to be generated according to a state of the secondregister 224.

The host interface circuit 222 may be configured to operate depending ona communication protocol applied to the interface circuit 130 of thehost 100 described with reference to FIG. 2. According to at least oneexample embodiment of the inventive concepts, an NVMe protocol forexchanging data in a PCIe manner may be applied to the host interfacecircuit 222.

The storage device interface circuit 226 may communicate with any otherstorage device (e.g., any one of the first and second storage devices 12and 15 of FIG. 1). For example, the communication protocol of thestorage device interface circuit 226 may be at least one of USB, SCSI,PCIe, NVMe, ATA, PATA, SATA, and SAS protocols.

The storage device interface circuit 226 may include an acknowledgmentmodule 227 for exchanging an acknowledgment signal with any otherstorage device. According to at least one example embodiment of theinventive concepts, in the case where the storage device 200 is a masterstorage device, the acknowledgment module 227 may receive anacknowledgment signal from a replica storage device. In this case, theacknowledgment signal may indicate that a command of the host 11 isprocessed by the replica storage device. According to at least anotherexample embodiment of the inventive concepts, in the case where thestorage device 200 is a replica storage device, the acknowledgmentmodule 227 may transmit an acknowledgment signal to a master storagedevice. In this case, the acknowledgment signal may indicate that acommand of the host 11 is processed in the controller 220 or a replicastorage device.

The storage device interface circuit 226 may further include a faultrecognition module 228 for exchanging an inquiry signal and a responsesignal with any other storage device. The fault recognition module 228may transmit an inquiry signal to any other storage device and mayreceive a response signal therefrom. Alternatively, the faultrecognition module 228 may receive an inquiry signal from any otherstorage device and may transmit a response signal thereto. The inquirysignal refers to a signal for determining whether an operation of anyother storage device goes down or whether a fault occurs, and theresponse signal refers to a signal transmitted as a response from astorage device receiving the inquiry signal. For example, the inquirysignal may be referred to as a “heart beat signal”. According to atleast one example embodiment of the inventive concepts, theacknowledgment module 227 and fault recognition module 228 are separatedfrom each other. However, according to at least some example embodimentsof the inventive concepts, the acknowledgment module 227 and faultrecognition module 228 may be implemented in a single integrated circuitor may be implemented within the controller 220 in the form of software.

The buffer manager 229 controls read and write operations of the buffermemory 240. For example, the buffer manager 229 may temporarily storewrite data or read data for the memory devices 211 to 213 in the buffermemory 240. The buffer manager 229 may manage an area of the buffermemory 240 under control of the processor 221.

The internal memory interface circuit 230 may exchange data with thememory devices 211 to 213. The internal memory interface circuit 230 maywrite data from the buffer memory 240 in the memory devices 211 to 213through channels CH1 to CH3. Afterwards, read data output from thememory devices 211 to 213 through the channels CH1 to CH3 may becollected by the internal memory interface circuit 230. The collecteddata may be transmitted to the host 100 after being stored in the buffermemory 240 or may be directly transmitted to the host 100.

According to at least one example embodiment of the inventive concepts,internal components (the processor 221, the host interface circuit 222,the first to third registers 223 to 225, the storage device interfacecircuit 226, the acknowledgment module 227, the fault recognition module228, the buffer manager 229, and the internal memory interface circuit230) of the controller 220 may be separated and implemented asillustrated in FIG. 3.

According to at least another example embodiment of the inventiveconcepts, unlike illustration, the internal components of the controller220 may be integrated and implemented on a single integrated circuitsuch as a system on chip (SoC), an application specific integratedcircuit (ASIC), or a field programmable gate array (FPGA). In this case,the internal components illustrated in FIG. 3 may be implemented in theform of software.

The buffer memory 240 operates as a buffer memory or a cache of thestorage device 200. For example, the buffer memory 240 may temporarilystore data received from the host 11 or data output from the memorydevices 211 to 213, or may temporarily store metadata (e.g., mappingtables) of the memory devices 211 to 213. The buffer memory 240 mayinclude a volatile memory such as a DRAM or an SRAM and may beconfigured to have an input/output speed faster than an input/outputspeed of the memory devices 211 to 213.

According to at least another example embodiment of the inventiveconcepts, the memory devices 211 to 213, the controller 220, and thebuffer memory 240 may be integrated in a single semiconductor device.According to at least one example embodiment of the inventive concepts,the memory devices 211 to 213, the controller 220, and the buffer memory240 may be integrated in a single semiconductor device to constitute asolid state drive (SSD). The memory devices 211 to 213, the controller220, and the buffer memory 240 may be integrated in a singlesemiconductor device to constitute a memory card. For example, thememory devices 211 to 213, the controller 220, and the buffer memory 240may be integrated in a single semiconductor device to constitute amemory card such as a PC card (a personal computer memory cardinternational association (PCMCIA) card), a compact flash card (CF), asmart media card (SM, SMC), a memory stick, a multimedia card (MMC,RS-MMC, MMCmicro, eMMC), an SD card (SD, miniSD, microSD, SDHC), oruniversal flash storage (UFS).

According to at least one example embodiment of the inventive concepts,the controller 220 may include or be implemented by one or more circuitsor circuitry (e.g., hardware) specifically structured to carry outand/or control any or all of the operations described in the presentdisclosure as being performed by the controller 220 (or an elementthereof). According to at least one example embodiment of the inventiveconcepts, the controller 220 may include or be implemented by a workingmemory and one or more processors executing computer-readable code(e.g., software and/or firmware) that is stored in the working memoryand includes instructions for causing the one or more processors tocarry out and/or control some or all of the operations described hereinas being performed by the controller 220 (or an element thereof).According to at least one example embodiment of the inventive concepts,the controller 220 may be implemented by, for example, a combination ofthe above-referenced hardware and one or more processors executingcomputer-readable code.

Configurations of the host 11 and the first and second storage devices12 and 15 described in FIG. 1 are described with reference to FIGS. 2and 3. A multicast communication method between the host 11 and thefirst and second storage devices 12 and 15 will be described below.

FIG. 4 is a flowchart illustrating a multicast communication methodbetween a host and storage devices, according to at least some exampleembodiments of the inventive concepts. FIG. 4 will be described withreference to FIGS. 1 to 3. In FIG. 4, it is assumed that a first storagedevice 310 is a master storage device and a second storage device 320 isa replica storage device. The first storage device 310 may include afirst controller 312, and the second storage device 320 may include asecond controller 322. Configurations of the first and secondcontrollers 312 and 322 may be substantially the same as theconfiguration of the controller 220 of FIG. 3. Also, the first andsecond storage devices 310 and 320 may be separated and implemented ormay be integrated and implemented in a single integrated device.

In operation S105, the host 100 may generate a command for storing datain the first and second storage devices 310 and 320 or reading data fromthe first and second storage devices 310 and 320 and may write thecommand in a submission queue (SQ) entry. The host 100 may update a tailpointer of a submission queue SQ allocated to the host memory 120.

In operation S110, the host 100 may update registers (e.g., the firstregister 223 of FIG. 3) of the first and second controllers 312 and 322,which store the submission queue tail doorbell SQTDBL, for notifying thefirst and second storage devices 310 and 320 that a new command iswritten in the submission queue SQ.

In operation S115, each of the first and second controllers 312 and 322may fetch the submission queue entry. The first and second storagedevices 310 and 320 may fetch a command that the host 100 generates, inparallel. Accordingly, the command that the host 100 generates may betransmitted to the first and second storage devices 310 and 320 in amulticasting manner. Afterwards, the first and second controllers 312and 322 may process the fetched command in parallel.

According to at least one example embodiment of the inventive concepts,one or more submission queue entries may be sequentially fetched when acommand is fetched by the first and second controllers 312 and 322. Inmore detail, the first and second controllers 312 and 322 maysequentially fetch commands stored from a submission queue head to asubmission queue tail in order.

In operation S120 and operation S125, the first and second controllers312 and 322 may respectively determine how to process the command,depending on a logical block address (LBA). The logical block addressmay be information included in the fetched command. The logical blockaddress may indicate information about a location where data are storedand may be referred to as a “logical address”.

Each of the first and second controllers 312 and 322 may determine itsown role depending on a logical block address included in the command.Here, a role of a storage device may be classified as a role of a masterstorage device or a role of a replica storage device. As illustrated inFIG. 4, the first controller 312 may determine, as its own role, a roleof a master storage device on the command fetched from the submissionqueue SQ, depending on a logical block address included in the fetchedcommand. As in the above description, the second controller 322 maydetermine, as its own role, a role of a replica storage device on thecommand fetched from the submission queue SQ, depending on a logicalblock address included in the fetched command. An operation in which acontroller determines a role by using a logical block address will bedescribed with reference to table 1.

In operation S121 and operation S126, the first and second controllers312 and 322 may respectively execute an operation corresponding to thefetched command depending on the logical block address and may processthe fetched command. For example, if the fetched command is a writecommand, each of the first and second controllers 312 and 322 may storedata provided from the host 100 in a memory device. For example, if thefetched command is a read command, each of the first and secondcontrollers 312 and 322 may read data requested by the host 100 from thememory devices 211 to 213 (refer to FIG. 3). Commands stored in thesubmission queue SQ may be processed in a fetched order or may not beprocessed in a fetched order.

In operation S130, the second controller 322 may transmit anacknowledgment signal to the first controller 312. In this case, theacknowledgment signal may indicate that the command that the host 100generates is processed by the second storage device 320 or the secondcontroller 322. The first controller 312 may receive the acknowledgmentsignal from the second controller 322 and may determine that commandprocessing of a replica storage device (e.g., the second storage device320) is completed. That is, through operation S130, the first controller312 may determine that the command that the host 100 generates isprocessed by the first and second storage devices 310 and 320.

In operation S135, the first controller 312 may write a completion queueentry or completion information for notifying completion of the commandfetched from the submission queue SQ. The collision event that the firstand second controllers 312 and 322 access the completion queue CQ at thesame time may not occur in operation S135. If the acknowledgment signalis received in operation S130, the first controller 312 may transmitcompletion information of the fetched command to the host 100. Since thesecond storage device 320 is a replica storage device, the secondcontroller 322 may not access the completion queue CQ. According to atleast one example embodiment of the inventive concepts, the completionqueue entry may be 16 bytes in size and may include a submission queueidentifier SQID, a submission queue head pointer SQHD, a status fieldSF, a phase tag P, a command identifier CID, etc.

According to at least some example embodiments of the inventiveconcepts, only a controller (the first controller 312) of a masterstorage device may access the completion queue CQ. Accordingly, thefirst controller 312 may access the completion queue CQ, while thesecond controller 322 may not access the completion queue CQ.Accordingly, even though the host 100 multicasts a command, thecollision event that the first and second controllers 312 and 322 accessthe completion queue CQ at the same time may not occur.

In operation S140, the first controller 312 may generate an interruptand may transmit the interrupt to the host 100. The interrupt may be apin-based signal or may be transmitted in a message signaled interrupt(MSI) manner or an MSI-X manner.

In operation S145, the host 100 may receive the interrupt from the firstcontroller 312 and may process a completion queue entry or completioninformation. In more detail, the host 100 may perform an interruptservice routine. If a command requested to the first and second storagedevices 310 and 320 is normally processed, the host 100 may newlygenerate a next command associated with the completed command. However,in the case where the requested command is not normally processed, thehost 100 may again generate a command or may perform an operation ofrecovering an error.

In operation S150, the host 100 may update registers (e.g., the secondregister 224 of FIG. 3) of the first and second controllers 312 and 322,which store the completion queue head doorbell CQHDB, for notifying thefirst and second storage devices 310 and 320 that the completion queueentry or completion information is processed.

According to at least one example embodiment of the inventive concepts,unlike illustration, depending on a logical block address of a command,the first storage device 310 may be a replica storage device, and thesecond storage device 320 may be a master storage device. In this case,operation S130 may be performed by the first controller 312, andoperation S135 and operation S140 may be performed by the secondcontroller 322. Also, the second controller 322 may access thecompletion queue CQ, while the first controller 312 may not access thecompletion queue CQ.

FIG. 5 is a flowchart illustrating a multicast communication methodbetween a host and storage devices, according to at least some exampleembodiments of the inventive concepts. FIG. 5 will be described withreference to FIGS. 1 to 4. Referring to FIG. 5, the host 100 may furthermulticast a command to a third storage device 330 as well as the firstand second storage devices 310 and 320. In FIG. 5, it is assumed thatthe first storage device 310 is a master storage device, the secondstorage device 320 is a replica storage device, and the third storagedevice 330 is an idle storage device. The idle storage device may referto a device that does not perform any task on a corresponding command. Arole of a storage device may further include a role of the idle storagedevice.

The first storage device 310 may include the first controller 312, thesecond storage device 320 may include the second controller 322, and thethird storage device 330 may include a third controller 332.Configurations of the first, second, and third controllers 312, 322, and332 may be substantially the same as the configuration of the controller220 of FIG. 3. Also, the first to third storage devices 310 to 330 maybe separated and implemented, or may be integrated and implemented in asingle integrated circuit.

Operation S205 to operation S215 are substantially the same as operationS105 to operation S115 of FIG. 4. However, the host 100 may furtherupdate a register (e.g., the first register 223 of FIG. 3) of the thirdcontroller 332, which stores the submission queue tail doorbell SQTDBL,and the third controller 332 may fetch a submission queue entry.

Operation S220 and operation S225 are substantially the same asoperation S120 and operation S125 of FIG. 4. In operation S230, thethird controller 332 may determine how to process a command depending ona logical block address. As illustrated in FIG. 5, the third controller332 may determine, as its own role, a role of an idle storage device onthe command fetched from the submission queue SQ, depending on a logicalblock address included in the fetched command. For example, each of thefirst, second, and third controllers 312, 322, and 332 may determinewhether to perform an operation or task corresponding to a command,depending on a logical block address.

Operation S221 and operation S226 are substantially the same asoperation S121 and operation S126 of FIG. 4. In operation S231, thethird controller 332 may not perform any task on the fetched command.

In operation S235, the second controller 322 may transmit anacknowledgment signal to the first controller 312. Also, the thirdcontroller 332 may transmit an acknowledgment signal to the firstcontroller 312. Since there is no role assigned to the third controller332 with regard to the fetched command, the third controller 332 may notperform an operation corresponding to the fetched command. The thirdcontroller 332 may not perform an operation corresponding to the fetchedcommand and may transmit an acknowledgment signal indicating that thefetched command is processed, to the first controller 312.

The first controller 312 may receive the acknowledgment signals form thesecond and third controllers 322 and 332, and may determine that commandprocessing of storage devices fetching a command from the host 100 iscompleted. One replica storage device and one idle storage device areillustrated in FIG. 5. However, at least some example embodiments of theinventive concepts may not be limited thereto. For example, the host 100may multicast a command to storage devices, the number of which is morethan illustrated. The first controller 312 may receive acknowledgmentsignals from storage devices fetching a command from the host 100 andmay count the number of the received acknowledgment signals. The firstcontroller 312 may determine whether the command of the host 100 isprocessed, based on the counting result.

Operation S240 to operation S255 are substantially the same as operationS135 to operation S150 of FIG. 4. The collision event that the first tothird controllers 312, 322, and 332 access the completion queue CQ atthe same time may not occur in operation S240. The host 100 may furtherupdate a register (e.g., the second register 224 of FIG. 3) of the thirdcontrollers 332, which stores the completion queue head doorbell CQHDBL,for notifying the third storage device 330 that the completion queueentry or completion information is processed.

According to at least one example embodiment of the inventive concepts,unlike illustration, depending on a logical block address of a commandgenerated by the host 100, the first storage device 310 may be a replicastorage device or an idle storage device, the second storage device 320may be a master storage device or an idle storage device, and the thirdstorage device 330 may be a master storage device or a replica storagedevice.

FIG. 6 is a flowchart illustrating a multicast communication methodbetween a host and storage devices, according to at least some exampleembodiments of the inventive concepts. FIG. 6 will be described withreference to FIGS. 1 to 5. Operation S305 and operation S320 tooperation S355 are substantially the same as operation S205 andoperation S215 to operation S250 of FIG. 5. A difference between FIGS. 5and 6 will be described below.

In operation S310, the host 100 may update only a register of the firstcontroller 312 without updating registers of the second and thirdcontrollers 322 and 332, which store the submission queue tail doorbellSQTDBL, for notifying the first to third storage devices 310 to 330 thata new command is written in the submission queue SQ.

In operation S315, the first controller 312 may update registers of thesecond and third controllers 322 and 332. The first controller 312 mayprovide the registers of the second and third controllers 322 and 332with a new submission queue tail doorbell updated by the host 100. Thatis, the first controller 312 may transmit information of a newsubmission queue to the second and third storage devices 320 and 330instead of the host 100.

In operation S360, to notify the first to third storage devices 310 to330 that the completion queue entry or completion information isprocessed, the host 100 may update only a register of the firstcontroller 312 without updating registers of the second and thirdcontrollers 322 and 332, which store the completion queue head doorbellCQHDBL.

In operation S365, the first controller 312 may update the registers ofthe second and third controllers 322 and 332 instead of the host 100.The first controller 312 may provide the registers of the second andthird controllers 322 and 332 with a new completion queue head doorbellupdated by the host 100. That is, the first controller 312 may transmitinformation of a new completion queue to the second and third storagedevices 320 and 330.

The first, second, and third controllers 312, 322, and 332 may fetch acommand from the submission queue SQ in parallel regardless of a mannerillustrated in FIG. 5 or a manner illustrated in FIG. 6. Even though thehost 100 updates only the register of the first controller 312, thefirst, second, and third controllers 312, 322, and 332 may fetch acommand of the submission queue SQ.

TABLE 1 Storage Device Storage Device Storage Device LBA MOD 3 (310)(320) (330) 0 0 Master Replica No Task (Idle) 1 1 No Task (Idle) MasterReplica 2 2 Replica No Task (Idle) Master 3 0 Master Replica No Task(Idle) 4 1 No Task (Idle) Master Replica

Table 1 shows results that controllers of storage devices according toat least some example embodiments of the inventive concepts determineroles for data according to a logical block address. Table 1 will bedescribed with reference to FIGS. 4 to 6. Table 1 shows results ofoperation S120 and operation S125 of FIG. 4, results of operation S220,S225, and S230 of FIG. 5, and results of operation S325, S330, and S335of FIG. 6.

Each of the first, second, and third controllers 312, 322, and 332 mayperform a modulo-N operation on a logical block address of a fetchedcommand. “N” may be determined based on the number of controllersfetching a command or the number of storage devices communicating with ahost according to a multicast communication protocol. In table 1, forexample, it is assumed that “N” is “3” indicating the number ofcontrollers.

Referring to table 1, the first controller 312 may perform a role of amaster storage device on data if the remainder of the modulo operationis “0”, may perform a role of an idle storage device on data if theremainder of the modulo operation is “1”, and may perform a role of areplica storage device on data if the remainder of the modulo operationis “2”. Roles of the second and third controllers 322 and 332 may bedetermined in a manner similar to the first controller 312.

From the point of view of data, for data which the logical block addressis “0”, the first controller 312 may store or copy the data as a masterstorage device, and the second controller 322 may store, copy, or backup the data as a replica storage device. In contrast, the thirdcontroller 332 may not perform any task on the data which the logicalblock address is “0”. For data having another logical block address, theroles of the first to third storage devices 310 to 330 may be determinedin a manner similar to the above-described manner.

From the point of view of the first controller 312, the first controller312 may in advance store a first setting value “0”, a second settingvalue “1”, and a third setting value “2”. The first to third settingvalues “0”, “1”, and “2” may be stored in the memory devices 211 to 213,the buffer memory 240, or an internal register (not illustrated) of thecontroller 220 of FIG. 3. The first to third setting values “0”, “1”,and “2” may be values determined in advance and may be shared by thesecond and third storage devices 320 and 330 through the storage deviceinterface circuit 226 of FIG. 3.

If the remainder of the modulo operation matches with the first settingvalue “0”, the first controller 312 may operate as a master storagedevice for a command. For example, if the remainder of the modulooperation matches with the first setting value “0”, the first controller312 may process a command (operation S121, operation S221, and operationS326) and may receive an acknowledgment signal from the secondcontroller 322 (operation S130, operation S235, and operation S340).

If the remainder of the modulo operation matches with the second settingvalue “1”, the first controller 312 may operate as an idle storagedevice for a command. For example, if the remainder of the modulooperation matches with the second setting value “1”, the firstcontroller 312 may not perform any operation on a command (operationS231 and operation S336) and may transmit an acknowledgment signal to amaster storage device (operation S235 and operation S340).

If the remainder of the modulo operation matches with the third settingvalue “2”, the first controller 312 may operate as a replica storagedevice for a command. For example, if the remainder of the modulooperation matches with the third setting value “2”, the first controller312 may process a command (operation S126, operation S226, and operationS331) and may transmit an acknowledgment signal to a master storagedevice (operation S130, operation S235, and operation S340).

According to at least one example embodiment of the inventive concepts,setting values stored in each of the first, second, and thirdcontrollers 312, 322, and 332 may be fixed values. According to at leastanother example embodiment of the inventive concepts, the setting valuesmay be dynamically changed. For example, the setting values stored ineach of the first, second, and third controllers 312, 322, and 332 maybe changed to adjust load balance of the first, second, and thirdcontrollers 312, 322, and 332.

FIG. 7 is a view illustrating a change of master devices for dataaccording to a change in setting values of a controller according to atleast some example embodiments of the inventive concepts. FIG. 7 will bedescribed with reference to FIGS. 5 and 6 and table 1. On the left sideof FIG. 7, the first storage device 310 may operate as a master storagedevice for data in which the remainder of a modulo-3 operation is “0”,the second storage device 320 may operate as a master storage device fordata in which the remainder of the modulo-3 operation is “1”, and thethird storage device 330 may operate as a master storage device for datain which the remainder of the modulo-3 operation is “2”.

Afterwards, in the case of reducing a load of the first storage device310 due to an increase in load of the first storage device 310, thefirst, second, and third controllers 312, 322, and 332 may communicatewith each other to change a manner of a modulo operation. For example,each of the first, second, and third controllers 312, 322, and 332 mayperform a modulo-5 operation. The first storage device 310 may operateas a master storage device if the remainder of the modulo-5 operation is“0”, the second storage device 320 may operate as a master storagedevice if the remainder of the modulo-5 operation is “1” or “3”, and thethird storage device 330 may operate as a master storage device if theremainder of the modulo-5 operation is “2” or “4”.

Referring to the right side of FIG. 7, as a mapping relationship of amaster storage device for data is updated, the load of the first storagedevice 310 may decrease. That is, the first, second, and thirdcontrollers 312, 322, and 332 may communicate with each other to changesetting values, a manner of a modulo operation, etc. The host 100 maynot participate in such a change process.

FIG. 8 is a flowchart illustrating a process of determining a newreplica storage device when an operation of a second storage deviceoperating as a replica storage device of first to third storage devicesgoes down. FIG. 8 will be described with reference to FIG. 5.

In operation S410, operation S420, and operation S430, the first,second, and third controllers 312, 322, and 332 may exchange inquirysignals and response signals with each other. As described above, aninquiry signal may be a signal for determining whether an operation ofany other storage device goes down or whether a fault occurs, and aresponse signal may be a signal transmitted as a response from a storagedevice receiving the inquiry signal. Operation S410, operation S420, andoperation S430 may be performed by the fault recognition modules 228(refer to FIG. 3) of the first, second, and third controllers 312, 322,and 332.

In operation S440, an operation of the second storage device 320 may godown due to any other cause. For example, the operation of the secondstorage device 320 may go down due to various causes such as collisionwith any other storage device, external impact, unstable power,lifespan, etc. In this case, the second storage device 320 may notgenerate response signals to inquiry signals of the first and thirdcontrollers 312 and 332. Accordingly, in response to failing to receiveresponse signals from the second storage device 320 in response toinquiry signals send from the first and third controllers 312 and 332,the first and third controllers 312 and 332 may determine that theoperation of the second storage device 320 has gone down.

In operation S450, the first controller 312 may determine the thirdstorage device 330 as a new replica storage device and may newly updatethe above-described setting values. Unlike illustration, if the numberof idle storage devices is 2 or more, the first controller 312 maydetermine any one of the idle storage devices as a new replica storagedevice. For example, the first controller 312 may determine a storagedevice, the load of which is relatively small, from among the two ormore idle storage devices as a new replica storage device.

FIG. 9 is a flowchart illustrating a multicast communication methodbetween a host and storage devices after a first controller determines athird storage device as a new replica storage device. FIG. 9 will bedescribed with reference to FIGS. 5 and 8. In FIG. 9, an operation ofthe second storage device 320 goes down (refer to operation S440).

Operation S505 to operation S515 are substantially the same as operationS205 to operation S215 of FIG. 5. However, since the operation of thesecond storage device 320 goes down, in operation S515, the secondcontroller 322 may fail to fetch a command from the submission queue SQ.

Operation S520 and operation S521 are substantially the same asoperation S220 and operation S221 of FIG. 5. The third storage device330 may perform operation S525 and operation S526 as a new replicastorage device. Operation S525 and operation S526 are substantially thesame as operation S225 and operation S226 of FIG. 5.

In operation S440 (refer to FIG. 8), if the fault recognition module 228of the first controller 312 determines that the operation of the secondstorage device 320 goes down, in operation S530, the first controller312 may receive an acknowledgment signal indicating that a command isprocessed by the third storage device 330, from the third storage device330 fetching the command from the host 100. Afterwards, operation S535to operation S550 are substantially the same as operation S240 tooperation S255 of FIG. 5.

FIG. 10 is a flowchart illustrating a process of determining a newmaster storage device when an operation of a first storage deviceoperating as a master storage device of first to third storage devicesgoes down. FIG. 10 will be described with reference to FIGS. 5 and 8.

Operation S610 to operation S630 are substantially the same as operationS410 to operation S430 of FIG. 8. In operation S640, an operation of thefirst storage device 310 may go down due to any other cause. In thiscase, the first storage device 310 may not generate response signals toinquiry signals of the second and third controllers 322 and 332.Accordingly, the second and third controllers 322 and 332 may determinethat the operation of the first storage device 310 operating as a masterstorage device goes down.

In operation S650, the second and third controllers 322 and 332 maydetermine any one of the second and third storage devices 320 and 330 asa new master storage device and may newly update the above-describedsetting values. For example, a storage device, the load of which isrelatively small, from among the second and third storage devices 320and 330 may be determined as a new master storage device. The other ofthe second and third storage devices 320 and 330 may be determined a newreplica storage device.

FIG. 11 is a flowchart illustrating a multicast communication methodbetween a host and storage devices after second and third controllersdetermine a second storage device as a new master storage device. FIG.11 will be described with reference to FIGS. 5 and 10. In FIG. 11, anoperation of the first storage device 310 may go down (refer tooperation S640), the second storage device 320 may be determined as anew master storage device by the second and third controllers 322 and332, and the third storage device 330 may be determined as a new replicastorage device thereby.

Operation S705 to operation S715 are substantially the same as operationS205 to operation S215 of FIG. 5. However, since the operation of thefirst storage device 310 goes down, in operation S715, the firstcontroller 312 may fail to fetch a command from the submission queue SQ.

The second storage device 320 may perform operation S720 and operationS721 as a new master storage device. Operation S720 and operation S721are substantially the same as operation S220 and operation S221 of FIG.5. The third storage device 330 may perform operation S725 and operationS726 as a new replica storage device. Operation S725 and operation S726may be substantially the same as operation S225 and operation S226 ofFIG. 5.

In operation S640 (refer to FIG. 10), if the fault recognition module228 of the second controller 322 determines that the operation of thefirst storage device 310 goes down, in operation S730, the secondcontroller 322 may receive an acknowledgment signal indicating that acommand is processed by the third storage device 330, from the thirdstorage device 330 fetching the command from the host 100. Also, if thefault recognition module 228 of the third controller 332 determines thatthe operation of the first storage device 310 goes down, the thirdcontroller 332 may transmit an acknowledgment signal to the secondstorage device 320 (a previous replica storage device and a currentmaster storage device) fetching a command of the host 100. Afterwards,operation S735 to operation S750 may be substantially the same asoperation S240 to operation S255 of FIG. 5.

According to at least another example embodiment of the inventiveconcepts, the third storage device 330 may be determined as a new masterstorage device, and the second storage device 320 may operate as areplica storage device without change. In this case, the thirdcontroller 332 may perform operation S720 and operation S721, and thesecond controller 322 may perform operation S725 and operation S726.

FIG. 12 is a view illustrating that a vector command is transmitted froma host to storage devices depending on a multicast communicationprotocol according to at least some example embodiments of the inventiveconcepts. Referring to FIG. 12, a storage system 400 may include a host410 and first and second storage devices 420 and 430. The host 410 maytransmit a vector command to the first and second storage devices 420and 430 depending on the above-described multicast communication method.

The vector command may be a list or a set of commands as illustrated inFIG. 12. A logical block address may be allocated to each command, and amemory block of a memory device may be specified by the logical blockaddress. The first and second storage devices 420 and 430 mayrespectively fetch a vector command generated by a host in paralleldepending on the multicast communication methods of FIGS. 4 to 11 andmay process the vector command.

FIG. 13 is a block diagram illustrating a storage system according to atleast some example embodiments of the inventive concepts. Referring toFIG. 13, a storage system 500 may include a host 510 and first andsecond storage devices 520 and 530. The host 510 may include a firstpair 512, a second pair 514, and a third pair 516.

The first pair 512 may be accessed by the first and second storagedevices 520 and 530. In more detail, the first and second storagedevices 520 and 530 may fetch a command from the submission queue SQ ofthe first pair 512, and a master storage device of the first and secondstorage devices 520 and 530 may write completion information in thecompletion queue CQ of the first pair 512. The first pair 512 may beshared by the first and second storage devices 520 and 530. The firststorage device 520 may include a first register 522, and the secondstorage device 530 may include a first register 532 so that a submissionqueue tail doorbell of the first pair 512 may be respectively written inthe first registers 522 and 532 by the host 510.

The second pair 514 may be accessed by the first storage device 520. Thesecond pair 514 may be a queue dedicated for the first storage device520. According to at least some example embodiments of the inventiveconcepts, the second pair 514 may be accessed only by the first storagedevice 520, and not by the second storage device 530. The first storagedevice 520 may include a second register 524 so that a submission queuetail doorbell of the second pair 514 may be written in the secondregister 524 by the host 510.

The third pair 516 may be accessed by the second storage device 530. Thethird pair 516 may be a queue dedicated for the second storage device530. According to at least some example embodiments of the inventiveconcepts, the third pair 516 may be accessed only by the second storagedevice 530, and not by the first storage device 520. The second storagedevice 530 may include a second register 534 so that a submission queuetail doorbell of the third pair 516 may be written in the secondregister 534 by the host 510.

That is, the host 510 may further include a dedicated queue (the secondpair 514) for the first storage device 520 and a dedicated queue (thethird pair 516) for the second storage device 530, as well as a sharingqueue (the first pair 512) for the first and second storage devices 520and 530.

FIG. 14 is a view illustrating a computing system according to at leastanother example embodiment of the inventive concepts. Referring to FIG.14, a storage system 600 may include first to fourth storage devices 610to 640. The first to fourth storage devices 610 to 640 may communicatewith each other according to a multicast communication protocolaccording to at least some example embodiments of the inventiveconcepts. That is, each of the first to fourth storage devices 610 to640 may perform an operation of the host 100 described with reference toFIGS. 1 to 11. Here, the first to fourth storage devices 610 to 640 maybe separated and implemented or may be integrated and implemented in asingle integrated circuit.

The first storage device 610 may include a first pair 612, the secondstorage device 620 may include a second pair 622, the third storagedevice 630 may include a third pair 632, and the fourth storage device640 may include a fourth pair 642. As in the first pair 512 of FIG. 13,the first, second, third, and fourth pairs 612, 622, 632, and 642 may beshared by other storage devices. The first pair 612 may be shared by thesecond to fourth storage devices 620 to 640, the second pair 622 may beshared by the first, third, and fourth storage devices 610, 630, and640, the third pair 632 may be shared by the first, second, and fourthstorage devices 610, 620, and 640, and the fourth pair 642 may be sharedby the first to third storage devices 610 to 630.

In accordance with the multicast communication protocol according to atleast some example embodiments of the inventive concepts, each of thefirst to fourth storage devices 610 to 640 may include only one pair ofsubmission and completion queues for communicating with the otherstorage devices, instead of including pairs of submission and completionqueues, the number of which is the same as the number of other storagedevices. For example, in the case where “N” storage devices communicatewith each other, a conventional P2P communication method needs “N×(N−1)”pairs of submission and completion queues. However, according to atleast some example embodiments of the inventive concepts, there is aneed for only “N” pairs of submission and completion queues.

FIG. 15 is a block diagram illustrating a user system to which amulticast communication method according to at least some exampleembodiments of the inventive concepts is applied. Referring to FIG. 15,a user system 700 includes an application processor 710, a memory module720, a network module 730, a storage device 740, and a user interface750.

The application processor 710 may drive components and an operatingsystem that are included in the user system 700. According to at leastone example embodiment of the inventive concepts, the applicationprocessor 710 may include controllers to control components of the usersystem 700, interfaces, graphics engines, etc. The application processor710 may be implemented with an SoC. The application processor 710 mayrefer to the host 11 of FIG. 1, the host 100 of FIG. 2, and a hostdescribed in FIGS. 4 to 6 and 8 to 13.

The memory module 720 may operate as a main memory, a working memory, abuffer memory, or a cache memory of the user system 700. The memorymodule 720 may include a high-speed memory device such as DDR4 SDRAM,LPDDR4 SDRAM, GDDRS SDRAM, or HBM.

The network module 730 may communicate with external devices. Forexample, the network module 730 may support wireless communications,such as code division multiple access (CDMA), global system for mobilecommunication (GSM), wideband CDMA (WCDMA), CDMA-2000, time divisionmultiple access (TDMA), long term evolution (LTE), Wimax, WLAN, UWB,Bluetooth, WI-DI, and the like. The network module 730 may be includedin the application processor 710.

The storage device 740 may store data. For example, the storage device740 may store data received from the application processor 710.Alternatively, the storage device 740 may transmit data stored thereinto the application processor 710. According to at least one exampleembodiment of the inventive concepts, the storage device 740 may referto the first and second storage devices 12 and 15 of FIG. 1, the storagedevice 200 of FIG. 3, the first and second storage devices 310 and 320of FIG. 4, the first to third storage devices 310 to 330 of FIG. 5, thefirst and second storage devices 420 and 430 of FIG. 12, the first andsecond storage devices 520 and 530 of FIG. 13, or the first to fourthstorage devices 610 to 640 of FIG. 14. Also, the storage device 740 mayoperate depending on the multicast communication method described withreference to FIGS. 1 to 14.

The user interface 750 may include interfaces that input data or aninstruction to the application processor 710 or output data to anexternal device. According to at least one example embodiment of theinventive concepts, the user interface 750 may include user inputinterfaces such as a keyboard, a keypad, buttons, a touch panel, a touchscreen, a touch pad, a touch ball, a camera, a microphone, a gyroscopesensor, a vibration sensor, and a piezoelectric sensor. The userinterface 750 may further include user output interfaces such as aliquid crystal display (LCD), an organic light-emitting diode (OLED)display device, an active matrix OLED (AMOLED) display device, alight-emitting diode (LED), a speaker, and a motor.

A multicast communication method according to at least some exampleembodiments of the inventive concepts may reduce latency due to aconventional P2P communication method.

With the multicast communication method according to at least someexample embodiments of the inventive concepts, a host may access storagedevices by using one submission queue and one completion queue.

With the multicast communication method according to at least someexample embodiments of the inventive concepts, storage devices maymutually adjust load balance.

With the multicast communication method according to at least someexample embodiments of the inventive concepts, it may be possible toflexibly cope with interruption or failure of the storage devices.

Example embodiments of the inventive concepts having thus beendescribed, it will be obvious that the same may be varied in many ways.Such variations are not to be regarded as a departure from the intendedspirit and scope of example embodiments of the inventive concepts, andall such modifications as would be obvious to one skilled in the art areintended to be included within the scope of the following claims.

What is claimed is:
 1. A storage device comprising: a memory device; anda controller, the controller being configured to, fetch a command from ahost, the command indicating a logical address, process the commandbased on the logical address, and receive, from a first replica storagedevice, an acknowledgment signal indicating that the command has beenprocessed by the first replica storage device.
 2. The storage device ofclaim 1, wherein the controller is further configured such that, inresponse to receiving the acknowledgment signal, the controllertransmits completion information of the command to the host.
 3. Thestorage device of claim 2, wherein the controller comprises: a firstregister; and a second register, and wherein the controller isconfigured to, store first information about a submission queue of thehost in the first register, transmit the first information to the firstreplica storage device, store second information about a completionqueue of the host in the second register, and transmit the secondinformation to the first replica storage device.
 4. The storage deviceof claim 1, wherein the controller is further configured to determinewhether the first replica storage has stopped operating by,transmitting, to the first replica storage device, an inquiry signal,and determining whether a response signal responding to the inquirysignal is received, from the first replica storage device, by thecontroller.
 5. The storage device of claim 4, wherein the controller isfurther configured such that, in response to determining that the firstreplica storage device has stopped operating, the controller determines,as a new replica storage device, a second replica storage device.
 6. Thestorage device of claim 4, wherein the controller is further configuredto communicate with the first replica storage device according to atleast one protocol from among a universal serial bus (USB) protocol, asmall computer system interface (SCSI) protocol, a PCI express protocol,NVM express (NVMe) protocol, an ATA protocol, a parallel ATA (PATA)protocol, a serial ATA (SATA) protocol, and a serial attached SCSI (SAS)protocol, and wherein the controller is configured such that thecontroller performs the transmitting of the inquiry signal and receivethe response signal based on the at least one protocol.
 7. The storagedevice of claim 1, wherein the controller is further configured suchthat, the controller performs a modulo operation on the logical address,the controller performs the processing of the command and the receivingof the acknowledgment signal in response to a remainder of the modulooperation having a first value.
 8. The storage device of claim 7,wherein the controller is further configured to communicate with thefirst replica storage device and change the first value.
 9. A storagedevice comprising: a memory device; and a controller, the controllerbeing configured to, fetch a command from a host, the command indicatinglogical address; process the command based on the logical address; andtransmit, to a master storage device, an acknowledgment signalindicating that the command has been processed.
 10. The storage deviceof claim 9, wherein the controller comprises: a first register; and asecond register, and wherein the controller is configured to, storefirst information about a submission queue of the host in the firstregister, update the first information based on information receivedfrom at least one of the host and the master storage device, storesecond information about a completion queue of the host in the secondregister, and update the second information based on informationreceived from at least one of the host and the master storage device.11. The storage device of claim 9, wherein the controller is furtherconfigured to determine whether the master storage device has stoppedoperating by, transmitting, to the master storage device, an inquirysignal, and determining whether a response signal responding to theinquiry signal is received, from the master storage device, by thecontroller.
 12. The storage device of claim 11, wherein the storagedevice is a first replica storage device, and the controller is furtherconfigured such that, in response to determining that the master storagedevice has stopped operating, the controller determines, as a new masterstorage device, a second replica storage device.
 13. The storage deviceof claim 11, wherein the storage device is a first replica storagedevice, and the controller is further configured such that, in responseto determining that the master storage device has stopped operating, thecontroller determines, as a new master storage device, the first replicastorage device, and the controller transmits completion information tothe host in response to receiving an acknowledgment signal from a secondreplica storage device, the completion information indicating thatprocessing of a command fetched from the host has been completed by thenew master device and the second replica storage device.
 14. The storagedevice of claim 9, wherein the controller is further configured suchthat, the controller performs a modulo operation on the logical address,the controller performs the processing of the command and thetransmitting of the acknowledgment signal in response to a remainder ofthe modulo operation having a first value.
 15. The storage device ofclaim 14, wherein the controller is further configured to communicatewith the master storage device and change the first value.
 16. Acommunication method of a host connected with first and second storagedevices, the method comprising: generating a command for controlling thefirst and second storage devices; causing the first and second storagedevices to fetch the command by updating at least a register of thefirst storage device; and receiving completion information of thecommand from the first storage device when the command is processed inthe second storage device and the second storage device transmits anacknowledgment signal indicating that the command is processed to thefirst storage device.
 17. The method of claim 16, further comprising:updating, by the host, a register of the second storage device whenupdating the register of the first storage device.
 18. The method ofclaim 16, wherein, when the host updates the register of the firststorage device, a register of the second storage device is updated bythe first storage device.
 19. The method of claim 16, wherein the hostincludes a submission queue configured to store the command and acompletion queue configured to store the completion information, andwherein a pair including the submission queue and the completion queueis shared by the first and second storage devices.
 20. The method ofclaim 16, further comprising: receiving the completion information ofthe command from the second storage device when the first storage devicestops operating, wherein the receiving of the completion information ofthe command from the second storage device comprises: transmitting, atthe second storage device, a signal for determining whether the firststorage device has stopped operating, to the first storage device.